The present invention relates to an intake passage construction for an internal combustion engine, and more particularly relates to an intake passage construction for a fuel injection type internal combustion engine.
In general, with regard to the design of intake systems for internal combustion engines, it has long been known that correct designing of the length of the intake passage which introduces gas into each cylinder of the engine is important for improving the volumetric efficiency and therefore the power output and the drivability of the engine, in order to take proper advantage of the intake pulsation effect and the intake inertia effect. Further, in the case of a multi cylinder internal combustion engine, it is also important to take account of and to minimize as far as possible the intake interference effect, in which interference between the various cylinders of the engine during their intake strokes reduces engine volumetric efficiency, thus reducing engine power output and drivability. Thus, the length of the intake passages should be determined in view of these various considerations, and quite often should ideally be quite long.
In the case of fuel injection engines, generally a surge tank is provided in the intake system of the engine, in order to reduce any surging of air that may tend to take place in this intake system, and individual intake tubes for each individual cylinder are extended from this surge tank, one to each of the cylinders. The relevant intake passage lengths in such a construction, for the intake pulsation effect, the intake inertia effect, and the intake interference effect, are the lengths of these individual intake tubes. Therefore, in order to obtain the best possible intake volumetric efficiency for the internal combustion engine, the lengths of these intake tubes must be set to appropriate values during the design process.
However, the space available in the engine room of an automobile is limited, and if a surge tank, which typically is quite large, must be fitted in this engine room, the freedom of design as to the location of said surge tank is quite limited, from the point of view of assembly convenience, servicing convenience, and the like. Further, the actual dimensional bulk of such a set of quite long intake tubes often also presents a similar problem of difficulty in design. Accordingly, it is often not possible to put the surge tank quite a long way away from the internal combustion engine, and in the prior art this has meant that it has not been possible to design the lengths of the intake tubes which lead to the various cylinders in the most advantageous way, so as to take advantage of the intake pulsation effect and of the intake inertia effect, and so as to minimize the intake interference effect.